# Isothermal Amplification Using Temperature-Controlled Frequency Mixing Magnetic Detection-Based Portable Field-Testing Platform

## TL;DR

This paper presents a portable platform for isothermal nucleic acid amplification and detection using a temperature-controlled magnetic sensor.

## Contribution

A new temperature-controlled sensor unit for FMMD using PWM and validated thermal models for RPA amplification in PoC settings.

## Key findings

- RPA performs similarly in the sensor unit as in a temperature-controlled water bath.
- A lumped parameter model accurately estimates sample temperature under varying ambient conditions.
- The platform is suitable for NA amplification and detection in resource-limited settings.

## Abstract

Sensitive magnetic nucleic acid (NA) detection via frequency mixing magnetic detection (FMMD) requires amplified NA samples for which a reliable temperature control is necessary. The feasibility of recombinase polymerase amplification (RPA) was studied within a newly integrated temperature-controlled sensor unit of a mobile FMMD based setup. It has been demonstrated that the inherently generated heat of the low frequency (LF) excitation signal of FMMD can be utilized and controlled by means of pulse width modulation (PWM). To test control performance in a point of care (PoC) setting with changing ambient conditions, a steady state and dynamic response model for the thermal behavior at the sample position of the sensor were developed. We confirmed that in the sensor unit of the FMMD device, RPA performs similar as in a temperature-controlled water bath. For narrow steady state temperature regions, a linear extrapolation suffices for estimation of the sample position temperature, based on the temperature feedback sensor for PWM control. For any other ambient conditions, we identified and validated a lumped parameter model (LPM) performing with high estimation accuracy. We expect that the method can be used for NA amplification and magnetic detection using FMMD in resource-limited settings.